Manufacture of rubber bonded abrasive articles



"l ing the materials between heavy metal rolls. Compounding ingredients known to the art 65 Patented Apr. 10, 1934 MANUFACTURE OF RUBBER BONDED ABRASIVE ARTICLES Harry C. Martin, Niagara Falls, N. Y., assignor to The Carborundum Company, Niagara Fails, N. Y., a corporation of Pennsylvania No Drawing. Application January it, 1928, Serial No. 245,032. Renewed 3 Claims. (Cl. Its-59) The present invention relates to the manufacacid, upon latex. While the mass is semi-solid ture of rubber bonded abrasive articles, and more and sufficiently viscous to hold the abrasive especially to the preparation of the rubber bond grains in suspension during working so that the and its incorporation withthe abrasive grains. abrasive articles can be properly formed without v 5 In the commercial manufacture of rubber gravity separation of the abrasive grains from to bonded abrasive articles, such as abrasive the binder, the mass is suificiently stirrable or wheels, the usual practice has been to mill the mobile so that the abrasive grains can be stirred abrasive grains and the vul'canizing' agents into into the mass, thus allowing the abrasive grains previously coagulated rubber by repeatedly passto be distributed through the mass.

This procedure requires considerable time and may be added to the rubber curd or to the latex crushes the abrasive grains into smaller sizes. before coagulation in order to impart their known Furthermore, it results in considerable wear on respective characteristics. In these cases, it is expensive machinery. sometimes necessary to use more fluid consisten- "IB 1 have found that a superior product may be cies than that mentioned above. Water to allow '20 made without the above disadvantages in manfor the absorptive efiect of such fillers may be ufacture, by starting with a different form of added therefore. In all cases the consistency of rubber which I may term rubber curd. The the mass is such as to maintain the grains in term rubber curd is used to designate a cursuspension.

dled form of rubber consisting of a viscous, In order that the articles may be vulcanized, a T5 mushy, semi-solid yet stirrable mass of a liquid, vulcanizing agent, such as sulphur, is used. This such as water, and rubber particles distributed is preferably introduced into the rubber latex therein. The rubber particles are so densely or before it is curdled. The sulphur is preferably closely distributed as to impart to the mass sufiiintroduced in the form of a water dispersion cient viscosity to keep the abrasive grains, such which may be made by grinding sulphur in water so as the granular silicon carbide or fused alumina, containing a small amount of a protective colloid, in suspension during the time that the mixture such as casein. The sulphur maybe ground until is being worked, for example, thirty minutes or the resulting particles of sulphur have a diammore. This viscosity is usually greater than 300 eter of less than .001 millimeters. Other possible seconds Saybolt at 70 Fahrenheit. methods are to add finely powdered sulphur to 85 The rubber exists in the form of particles the curd, or to mix the sulphur with the dry inwhich are approximately .002 millimeters in digredients and then add to the curd, or any other ameter and exhibit little or no Brownian movesuitable method. ment, as contrasted with the rubber as it exists In making an abrasive article, such as an in latex. Latex may be transformed into rubber abrasive wheel, the dispersed sulphur is mixed go curd by some curdling process which results in with the latex which is curdled. This curdling transforming the rubber from the latex form may be accomplished in the following manner. into the curdled form. This curdling may be A saturated solution of lead acetate is slowly produced by different methods, such for example, added with constant stirring to the latex, in an 40 as: amount equal to approximately 10% of the rubber 95 1. The neutralization of the negative electrical content of the latex. This produces a viscous, charges on the rubber particles by the addition mushy mass. Then the curdled mass is stirred of positively charged particles. with the abrasive grains. The rubber curd is 2. The removal of water by mechanical means, sufiiciently viscous as to overcome the separation such as by centrifuging to such an extent as to or gravity settling out of the grains which would 1'00 transform the latex into a curd. occur in case a thin and more mobile dispersion 3. The addition of salts such as lead acetate of rubber, such as untreated latex, were used. or aluminum sulphate. While it is preferred to carry the curdling of The curdling operation is similar in its action the latex to a point where the curdling alone to the coagulation of latex into crepe rubber, but will give the necessary viscosity to support the 5 it is not carried so far. The rubber particles of abrasive grains, the curdling may not be carried the rubber curd appear to be discrete, that is, to this point, but the latex may be partially they do not form a connected structure as in thickened by curdling and partially by the addithe fully coagulated or crepe rubber produced tion of some absorbent or thickening material by the full action of a coagulant, such as acetic such as wood flour, soap, glue, etc., to a consistency suflicient to prevent the segregation or settling out of the abrasive particles. Therefore, when I speak of curdling of the latex I do not mean that the curdling is necessarily carried to the point where it alone is depended upon to give the desired viscosity.

If desired, concentrated latex may be used. In concentrated latex water is removed, thus concentrating the rubber suspension, which because of the removal of the water is of a thicker consistency than the original latex. If concentrated latex be used, it should be thickened by a curdling operation or by the addition of some thickening material.

In making an abrasive article, such as a grinding wheel, the abrasive mixture may contain, as a typical example, seventy parts by weight of abrasive grains, four parts by weight of sulphur and eight parts by weight of rubber as rubber curd.

Then the wet mix is shaped into a blank by tamping into a mold. The blank is then dried in a gradually reduced pressure starting at atmospheric and finishing at about twenty-nine inches of mercury vacuum at a minimum temperature generally less than 160 Fahrenheit. An alternative humidity drying procedure may be fol lowed, or if desired, a pressing operation may be used to remove a portion of the Water. When the blank is dried, it is placed in a mold and heated to about the melting point of sulphur (115 Centigrade) under a pressure of about 100 pounds per square inch for about three to ten minutes. Following this slight pressure, a pressure of 5000 pounds per square inch is applied for about five minutes while the article is still held at a temperature of 115 centigrade. The article which is thus formed is then removed from the mold and vulcanized in the usual manner.

Instead of first making a blank and drying it, and then shaping the dried blank under pressure to the finished shape of the article, the mix itself may be brought to a condition in which it is moist, but without excess water. The article may be molded under pressure directly from this mix to its finished shape. The drying of the mix to this moist condition may be attained either by the removal of water from the mix or by its absorption by the ingredients of the mix.

While I have described the preferred procedure in carrying out my process, it is to be understood that the process is not limited to all of the herein described details or exact sequence of steps, but may be otherwise embodied and practiced within the scope of the following claims.

I claim:

1. The process of making rubber bonded abrasive articles, which comprises preparing a viscous, mushy, semi-solid yet stirrable mass of liquid and rubber so distributed therein as to thicken the mass sufficiently to hold the abrasive material in suspension during the mixing and forming of the article, mixing granular abrasive material with such mass, and forming the articles from the mixture in a mold, drying the articles at pressures less than atmospheric, and subjecting the dried articles to pressures sufficient to consolidate the rubber and abrasive grain.

2. The process of making rubber bonded abra sive articles, comprising preparing a viscous, mushy, semi-solid yet stirrable mass of liquid and rubber so distributed therein as to thicken the mass sufficiently to hold the abrasive material in suspension during the mixing, mixing granular abrasive material with such mass, shaping the articles from the mixture, and drying them.

3. The process of making rubber bonded abrasive articles, which comprises mixing abrasive particles with rubber curd and a vulcanizing agent, shaping the articles from the mixture and drying them, and vulcanizing them.

4. The process of making rubber bonded abrasive articles, which comprises concentrating latex, thickening the concentrated latex by means of a chemical coagulation and protecting the rubber particles so aggregated with a colloid sheath, mixing it with abrasive particles, and forming the articles from the mixture.

5. The process of making rubber bonded abrasive articles, which comprises forming a mix containing granular abrasive material, a vulcanizing agent and a viscous, mushy, semiolid yet stirrable mass of wateand rubber so distributed therein as to thicken the mass sufficiently to hold the abrasive material in suspension during theforming of the articles, shaping the articles from the mix, drying them, and vulcanizing them.

6. The process of making rubber bonded abrasive articles, which comprises forming a mixture containing abrasive grains, a vulcanizing agent and a viscous rubber emulsion containing rubber latex, forming the articles from the mixture, and

rying and vulcanizing them.

7. The process of making rubber bonded abrasive articles, which comprises adding to rubber latex a coagulant sufficient in amount to thicken the latex so that the abrasive grains may be mixed and held suspended therein, forming a mixture containing such thickened latex, abrasive grains and a vulcanizing agent, shaping the articles from the mixture, and drying and vulcanizing them.

8. The improvement in the manufacture of rubber bonded articles containing granular material comprising admixing abrasive grain and a vulcanizing agent with a fluid rubber mixture containing rubber latex, shaping the mixture to the desired form, and subsequently drying and vulcanizing the thus shaped article.

9. The improvement in the manufacture of rubber bonded abrasive articles comprising treating rubber latex with an agent of a character and in an amount to increase the consistency of the latex so that granular material may be uniformly and intimately mixed and maintained suspended therein, incorporating abrasive grain and a vulcanizing agent in the mixture and shaping substantially to the form desired, and subsequently drying and vulcanizing the thus shaped article.

10. The process of making rubber bonded abrasive articles, comprising making a mix containing abrasive grain, a vulcanizing agent and a viscous mushy yet stirrable mass containing water and rubber so distributed therein as to thicken the mass sufficiently to prevent separation of the mass and the abrasive grain during the operations of mixing and of removing Water, shaping abrasive articles therefrom and vulcanizing them, and removing water from the material subsequent to the mixing in of the abrasive grain and prior to the vulcanization of the articles.

11. The process of making rubber bonded abrasive articles, comprising making a mix containing abrasive grain, a vulcanizing agent and a viscous mushy yet stirrable mass containing water and rubber so distributed therein as to thicken the mass sufiiciently to prevent separation of the mass and abrasive grain during the operations of mixing and of removing water, removing water from the mix, shaping abrasive articles from the mix, and vulcanizing them.

12. The process of making rubber bonded abrasive articles, comprising making a mix containing abrasive grain, a vulcanizing agent and a viscous mushy yet stirrable mass containing water and rubber so distributed therein as to thicken the mass sufiiciently to prevent separation of the mass and the abrasive grain during the making and the drying of the mix, drying the mix, shaping abrasive articles from the dried mix, and vulcanizing them.

13. The process of making rubber bonded abrasive articles, comprising making a mix containing abrasive grain, a vulcanizing agent and a viscous mushy yet stirrable mass containing water and rubber so distributed therein as to thicken the mass sufliciently to prevent separation of the mass and the abrasive grain during the making of the mix and the shaping and drying of the articles, shaping abrasive articles from the mix, drying the shaped articles, and vulcanizing them.

14. The process of making rubber bonded abrasive articles which comprises mixing abrasive particles with a rubber curd and a vulcanizing agent,

shaping the articles from the resulting mixture of curd, vulcanizing agent and abrasive particles,

CERTIFICATE OF. CORRECTION.

Patent No. 1,953,984. April to, 1934.

HARRY G. MARTIN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, after line to,

insert the following as example 2:

2. The absorption of sulticient water by the addition of an absorbent material such as diatomaceous earth, to produce the curd; line 44, for the numeral 2" read 3; and line 47, for "3" read 4; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent ()flioe.

Signed and sealed this 15th day of May, A. D. 1934 Bryan M. Battey (Seal) Acting Commissioner of Patents, 

